1. Technical Field of the Invention
The present invention relates to a battery module made by connecting a plurality of rechargeable batteries so as to obtain a necessary power capacity.
2. Description of Related Art
FIG. 13 shows a conventional battery module made by connecting a plurality of cells and coupling them integrally so as to obtain a necessary power capacity. In this battery module, a plurality of cells 41 (41a to 41j) made of sealed alkaline rechargeable batteries as shown in FIG. 14 are arranged in a row with the long side walls of the cell cases 42 adjacent with each other. End plates 52 are placed against the outside of the cells 41a and 41j at the opposite ends, and the cells, together with the two end plates 52, 52, are bound together with binding strips 53, whereby the plurality of cells are coupled into an integral body.
In the cells 41, an electrode plate group 47, or elements for electromotive force, made by laminating negative plates and positive plates with intervening separators, is accommodated in a cell case 42 together with an electrolyte, and the opening of the cell case 42 is closed with a lid 46 provided with a safety vent 45. From the upper end of the positive plates on one side of the electrode plate group 47, leads 49 extend upward and are connected to a positive terminal 43 thereabove, and similarly, from the upper end of the negative plates on the other side of the electrode plate group, leads 49 extend upward and are connected to a negative terminal 44 thereabove. The positive terminal 43 and the negative terminal 44 are attached to the lid 46.
The positive terminals 43 and negative terminals 44 of neighboring cells 41, 41 that are coupled together are connected by connection plates 51, thereby connecting all cells 41 in series. When the cell cases 42 are coupled, ribs 48, which protrude vertically from the long side walls of the cell cases 42, are abutted against each other, so as to form coolant passages which extend in the vertical direction of the long side walls of the cell cases 42. The cells 41a to 41j are cooled by flowing air through these coolant passages.
However, in this conventional battery module, because the plurality of cells 41 are completely separate and sealed from each other, there was the following problem. When the internal pressure in some of the cells 41 rises due to variations in capacity or temperature of the cells 41, deterioration of the electrode plates of the cells 41 caused by oxidation is accelerated, which in turn leads to increased variations in the internal pressure and progress of deterioration between various cells 41. As a result, the balance of the condition of the electrode plates of the cells 41 in the battery module is disturbed, and inconveniences such as overcharging and over-discharging occur in some of the cells 41, which leads to a decrease in the lifetime of the battery module.
Moreover, safety vents 45 for releasing gas to the outside when the internal pressure in the cells 41 exceeds a certain value have to be provided for each of the cells 41, so that there was the problem that the number of safety vents 45 to be installed is large and the costs are high.
In view of these problems of the prior art, it is an object of the present invention to provide a battery module, by which the lifetime of the battery module can be extended by acquiring balance in the progress of deterioration of the electrode plates between various cells that constitute the battery module, and by which costs can be lowered by reducing the number of safety vents to be installed.
A battery module according to the present invention comprises an integrated battery case that is constituted by coupling together a plurality of cell cases into an integral body; and an integral lid member for closing open ends of the plurality of cell cases, wherein communicating paths are provided for communicating a predetermined number of neighboring cell cases with one another. Because the insides of the cell cases are mutually communicated through the communicating paths, the internal pressure in the cell cases becomes equal and gas that is generated in those cells whose deterioration is most advanced is absorbed by other cells, thereby suppressing the progress of oxidation deterioration of the most deteriorated cell and ensuring good balance in the internal pressure and the progress of deterioration between various cells, whereby the lifetime of the battery module is increased.
If the communicating paths are formed in the lid member, neighboring cell cases are communicated with one another without providing spaces for communicating paths in the cell case. Thus balance is acquired between various cells and the lifetime of the battery module can be increased similarly as above with a simple and compact configuration.
It is preferable that through holes be formed on the top face of the lid member at positions corresponding to abutting ends of adjacent cell cases, and that communicating lids formed with communicating paths for communicating these through holes be attached tightly to the top face of the lid member. Thereby, the communicating paths are arranged above the top face of the lid member, and transfer of the electrolyte between the cell cases can be prevented reliably.
If the communicating paths are formed by monolithic molding in the lid member, the number of parts can be reduced because the communicating lids become unnecessary, and since there are no fixing parts, the inner walls of the communicating path have a smooth surface, so that the electrolyte hardly adheres thereto and a short-circuit due to transfer of the electrolyte between the cell cases can be prevented. Also, because the communicating paths are formed by monolithic molding, high strength of the lid member against internal pressure can be achieved.
Partitions may be formed in the lid member such as to be bonded to the side walls of the cell cases of the integrated battery case, and to extend upward to the proximity of the height of the top face of the lid member, so as to form communicating paths in a portion above and on both sides of the partitions. While the cross section of the communicating paths above the partitions for letting gas flow can be made large, high strength of the lid member against internal pressure can be achieved, due to the communicating paths being formed by monolithic molding and due to these partitions. Moreover, transfer of the electrolyte between the cell cases can be prevented more reliably, because the communicating paths are formed near the top face of the lid member.
By making the surface of the communicating paths of a material that is repellent against an electrolyte, or by providing a projection in the communicating paths, transfer of the electrolyte between the cell cases can be prevented more reliably.
By providing a single safety vent in the lid member for a plurality of cell cases mutually communicated, the number of safety vents to be installed can be reduced, whereby cost can be decreased.
Furthermore, by making the thickness of shorter side walls between adjacent cell cases in the integrated battery case smaller than the thickness of outer side walls of the two cell cases located at either end of the battery module, the volume density of the battery module as a whole can be increased and the connection resistance between the cells can be lowered.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.